These days, environmental regulations are being increasingly tightened on a global scale, among which fuel efficiency regulations and exhaust emission regulations for automobiles are especially being further tightened. Demands for tightening of the regulations are derived from environmental issues such as global warming and resource conservation due to a concern for depletion of petroleum resources.
Meanwhile, plants living on the earth absorb carbon dioxide in the air, water and sunlight to photosynthetically generate carbohydrate and oxygen. What is called, biofuel, which is manufactured from plant-based plant oil, has been gathering remarkable attentions because of its effects on reduction of carbon dioxide (a main cause of global warming) and reduction of atmospheric contaminants emitted from automobiles. In line with an idea of carbon neutral advocating that carbon dioxide generated due to combustion of plant biomass is not counted as a contributor to an increase of the global warming gas, ratio at which the biofuel is mixed in hydrocarbon fuel is expected to be increased in the future (cf. Non-Patent Document 1:).    Non-Patent Document 1: Koji YAMANE, From Biodiesel Deep Fryer to Fuel Tank, (Tokyo-Tosho-Shuppankai, May of 2006)